1. Field of the Invention
The present invention relates a camera's exposure control system capable of performing exposure computations for exposure control, simultaneously performing these exposure computations, for example, by means of camera accessory or adaptor, such as an interchanageable camera back lid for the exposure control.
2. Description of the Prior Art
In recent years, photographic cameras with exposure control devices in the camera main body that have plural exposure control modes, such as an aperture priority automatic exposure control mode (A mode), a shutter speed priority automatic exposure control mode (S mode), and a programmed automatic exposure control mode (P mode), and that freely permit the photographer to select a desired mode have been proposed, and some have already been placed on the market. The kinds of exposure control modes that can be incorporated into a camera are, however, limited. For users who wish to take photographs by using exposure control modes other than those incorporated in the camera's main body, a camera with an interchangeable back lid on which plural programmed lines (including S mode and A mode) are set and displayed by means of the programmed line setting means so that a desirable mode can be selected from the available modes is proposed in Japanese laid-open patent publications No. 54-139732 and U.S. Pat. No. 4,455,068.
Conventional cameras proposed have a back lid mounted with only a data setting device, so the microcomputer incorporated in the camera body is programmed to meet the needs for different settings. For this reason, a microcomputer with a large program capacity must be used, resulting in an expensive camera body. Further, users who do not wish to buy such a camera with plural exposure computation functions are nevertheless compelled to purchase it. Although the equipment or the system related to the above devices are proposed in Japanese laid-open patent publication No. Sho Sho 54-58529 and U.S. Pat. Nos. 4,165,929, 4,165,929 and 4,206,987 all are not capable of being generally used, or they are insufficient in their flexibility.